Hi, On Sun, Dec 6, 2015 at 6:50 PM, Doug Anderson <diand...@chromium.org> wrote: > Chris, > > On Sun, Dec 6, 2015 at 5:33 PM, Chris Zhong <z...@rock-chips.com> wrote: >> Hi Doug >> >> RK808 has a shadowed register for saving a "frozen" RTC time. >> When we setting "GET_TIME" to 1, the time will save in this shadowed >> register. So if we do not set the "GET_TIME", we always get the last time. >> >> read the old time before "get_time", and then read the time again for new >> time. If the old time earlier than 12.1 && new time later than 12.1, we >> should >> +1 day for the correct rtc time. >> >> On the other hand, we should set the "GET_TIME" after rk808_rtc_set_time, >> for restore the time before suspend/shut_down. > > Ah, good idea using the shadow registers. The whole point of the > shadow registers is to enable atomic read of time, right? So if the > clock ticks as you are reading 23:59:59 you don't end up reading > 23:59:00 or 24:59:59 (you'll get either 23:59:59 or 24:00:00). So > right, time read will now be: > > 1. Read GET_TIME. Confirm it's 1. > 2. Read the time. > 3. Set GET_TIME to 0. > 4. Set GET_TIME to 1. > 5. Read the time. > > If time from #2 < 11/31 and time from #5 >= 11/31 then we do the > adjust. If GET_TIME wasn't 1 in step #1 then we won't do any > adjusting unless the time is actually 11/31. > > Between steps #4 and #5 we'll need to add a small delay since old code > used to use the setting to 0 as a delay (as commented). > > We should presumably always leave GET_TIME as 1 unless we're actively > reading the time for the most reliability. Also, if we've already > read the time this bootup, we can certainly optimize the above by > skipping #1 and #2.
Oh, but also we still need to know whether to adjust the alarm. I think you said that all existing rk808 chips have this bug and that you'll set a bit (to be determined later) if/when this bug is fixed. So we still need to assume that all rk808 chips have this bug... -Doug -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/